Monitoring the neurological state of a patient

Abstract

The invention relates to monitoring the neurological state of a patient. In the method invention, both cortex- and subcortex-related biosignal data are obtained from the patient, the subcortex-related biosignal data including at least bioimpedance signal data. A first indicator is calculated based on the cortex-related biosignal data, the first indicator being indicative of cortical activity in the patient and a set of indicators is calculated based on the subcortex-related biosignal data indicative of subcortical activity in the patient, the set of indicators including at least a second indicator calculated based on the bioimpedance signal data. A composite indication is then produced based on the first indicator and on the set of indicators. The invention also concerns an apparatus and a sensor for monitoring the neurological state of the patient.

Description

FIELD OF THE INVENTION[0001]The present invention relates generally to a method and apparatus for monitoring the neurological state of a patient. As discussed below, neurological state here refers to a state which is described by indicators indicative of the quality or adequacy of anesthesia or sedation applied to the patient. One application of the method and apparatus is thus monitoring the condition of a patient under anesthesia or sedation. The invention also relates to a sensor for obtaining the biosignal data needed for the monitoring.BACKGROUND OF THE INVENTION[0002]In living organisms, biological processes generate different types of output signals, which are generally referred to as biosignals. Biosignals may be electrical, mechanical or chemical.[0003]Bioelectricity is a broad field including measurements of biopotentials and bioimpedance. Biopotentials cover electricity created in life processes internal in tissues, while in bioimpedance measurements electric currents are...

AI Technical Summary

Problems solved by technology

However, these passive properties can also be related to electrical or other processes internal in tissues, even though the measurement does not directly utilize the electricity generated internally in tissues.

Specifically, this has become an issue, both scientifically and commercially, in the context of measuring the depth of anesthesia during surgery.

Awareness during surgery with insufficient analgesia may lead to a post-traumatic stress disorder.

Low quality pre- and intra-operative analgesia makes it difficult to select the optimal pain management strategy later on.

More specifically, it may cause exposure to unwanted side effects during the recovery from the surgery.

Too light an anesthesia with insufficient hypnosis causes traumatic experiences both for the patient and for the anesthesia personnel.

From economical point of view, too deep an anesthesia may cause increased perioperative costs through extra use of drugs and time, and also extended time required for post-operative care.

Too deep a sedation may also cause complications and prolong the usage time of expensive facilities, such as the intensive care theater.

The assessment, measurement, or control of the different components of anaesthesia is ‘a line drawn in water’, as the drugs used in anaesthesia are often unspecific and influence many components simultaneously.

As to the central nervous system (CNS), the assessment or measurement of the suppression of the sub-cortical activity and integrity is far more unsatisfactory.

No commercial devices exist for this purpose.

However, the above-mentioned dependency on the medication of the patient may render the method unusable in certain situations.

As the (facial) electromyography signal is affected by neuro-muscular blocking agents (NMBAs), which suppress signaling at the nerve-muscle junctions, the EMG component of the measurement may vanish and render the method unusable, if the medication of the patient includes neuro-muscular blocking agents.

The fEMG signal is thus activated after non-noxious stimulation such as auditory stimulation and it is difficult to assess if any noxious components are present in the facial muscle response.

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